Method and product for varying the thickening time of a class G cement used in completing a subterranean wellbore

ABSTRACT

Spent Claus catalyst having a high alumina content is used as an ingredient in the manufacture of Portland cements in place of all or a portion of a conventional source of alumina. The spent Claus catalyst is preferably of a small particle size and can be ground to the desired fineness before mixing with the other ingredients that are heated in a conventional kiln to produce the cement composition. Finely ground spent Claus catalyst can also be used as an additive at levels of 0.1% to 2% by weight to increase the thickening time of shallow casing cement slurries.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/631,823filed Jun. 20, 2007, now U.S. Pat. No. 8,029,618, which was the NationalStage of International Application No. PCT/US2005/034339, filed on Sep.21, 2005, which claims the benefit of U.S. Provisional Application No.60/611,769, filed Sep. 21, 2004, the contents of all of which areincorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to the use of spent Claus catalyst particles inthe production of Portland cement.

BACKGROUND OF THE INVENTION

The Claus process continues to be the most widely used process worldwideto convert hydrogen sulfide that has been stripped from acid gas orrefinery off-gas streams to elemental sulfur. It consists of a two-stageprocess: the first process stage is thermal and the second stage iscatalytic. During the thermal process, the H₂S is partially oxidizedwith air in a reaction furnace at high temperatures, e.g., from1000°-1400° C. Sulfur is formed, but some H₂S remains unreacted and SO₂is also formed, as depicted below:2H₂S+3O₂→2SO₂+2H₂O  (I)

During the catalytic process, the remaining H₂S is reacted with the SO₂at lower temperatures, i.e., about 200°-350° C., over a catalyst toproduce additional elemental sulfur, as follows:2H₂S+SO₂→3S_(x)+2H₂O  (II)

The Claus catalyst which offers improved sulfur conversion overspherical activated bauxite, or alumina, has high surface area, lowdensity and high macroporosity. These properties provide maximumactivity for the conversion of sulfur compounds. The art relating to theproduction of Claus catalysts is well developed, as shown, for example,in U.S. Pat. No. 4,364,858 and the numerous patents cited and discussedthere. However, the reaction does not go to completion, even with thebest catalyst. For this reason, two or three catalytic stages are used,with sulfur being removed between the stages.

Claus catalyst is deactivated due to lay down of coke andsulfur-containing species causing lowering of sulfur recovery and alsopolluting the atmosphere by releasing excessive amounts of sulfurdioxide during acid gas flaring. The deactivation of the Claus catalystis caused by a variety of factors, such as the presence of accompanyinghydrocarbons, particularly of C-5's and benzene, toluene and xylenes.Sour gases are prone to lay down coke on Claus catalyst due to thermalcracking in the split-flow mode.

Hundreds of tons/year of spent Claus catalyst are produced by gasprocessing plants, gas-oil separation plants (GOSPs) and natural liquidgas fractionation facilities due to frequent replacement of the aluminacatalyst beds. In many instances, the spent catalyst has been disposedof by dumping it in a landfill. The cost of landfilling spent Clauscatalyst is generally minimal where the land is available andinexpensive, the principal cost being its transportation.

National and international regulations have provided increasedopportunities and economic incentives for the petroleum and gasprocessing industries to implement waste reduction programs for thepurpose of enhancing the environment. The incentives for wasteminimization on an international basis have been increased by the ban onthe land disposal of untreated wastes from the petroleum industry. Asthe complexity and cost of waste management and disposal increases,waste minimization becomes a significant priority for industry andgovernment.

The goal of reducing waste material from industrial processes requiringdisposal can be accomplished either by regeneration of the material orby finding a new and economical use for the spent Claus catalyst wastematerial.

In some instances, the regeneration treatment cost has been found to bemore expensive than purchasing fresh catalyst and, therefore,regeneration was not economically viable.

Other proposals for utilizing spend catalytic materials in anenvironmentally acceptable manner can also be found in the prior art.For example, U.S. Pat. No. 5,032,548 and U.S. Pat. No. 5,096,498recommend the use of catalyst particles within a prescribed size rangeas a base in large construction projects, such as roads and levees.However, the spent catalyst must also be mixed with hydrated lime,Portland cement and other binders.

The use of spent catalyst fines admixed with concrete is disclosed inU.S. Pat. No. 4,231,801. The use of catalyst particles in the processfor manufacturing a Portland cement prior to the burning step isdisclosed, but it also teaches the addition of an agglomeratingmaterial.

It is therefore a principal object of the present invention to provide ameans of economically and beneficially utilizing the spent Clauscatalyst in order to provide an alternative to landfill disposal.

A further object of the invention is to provide new uses for spent Clauscatalyst that will have a significant favorable environmental andcost-saving impact on those industries that must dispose of the spentcatalyst.

SUMMARY OF THE INVENTION

The above objects and other advantages are achieved by the method andcomposition of the invention that broadly contemplates the addition ofspent Claus catalyst as an additive, or raw material, in the manufactureof Type I, II and V Portland cement.

The spent Claus catalyst is comprised principally of alumina, or Al₂O₃.This compound is an essential additive for the production of Portlandcement, which contains about 5% of alumina.

Portland cement is composed of lime or limestone, alumina, iron oxideand silica and is manufactured by burning all of these materials inpre-determined is proportions in a rotary kiln at temperatures in therange of 1450°-1500° C. Small amounts of magnesia, sodium, potassium andsulfur are also present. The principal reactions are represented by thefollowing:CaCO₃(limestone)→CaO+CO7CaO+Al₂Si₂O₇→Ca₂SiO₄+Ca₃Al₂O₆

The product formed in the kiln is known as clinker. The clinker isallowed to cool and then is ground to a fine powder along with a smallpercentage (4-5%) of gypsum or its derivatives. This finely blendedpowder is known as Portland cement.

The silica can be provided from a number of sources, including clay,sand, quartz, and other materials that are well known in the art. Aportion of the alumina-containing material is replaced by the spentClaus catalyst.

Spent Claus catalyst utilization in the production of Portland cementwill provide significant environmental and cost-saving benefits sincethe volume of cement manufacturing and use in the areas where the spentClaus catalyst is generated will likely be sufficient to utilize all ora significant proportion of this waste material, thereby eliminating theneed for landfill disposal of the spent catalyst.

In this application of the invention, the spent catalyst may containresidual hydrocarbons that will be released and/or oxidized duringheating in the kin. Should tests of the finished cement and/or itsconcrete products indicate the presence of residual hydrocarbons, theend use applications should exclude closed structures used by personneland animals due to the potential presence of such hydrocarbons.Alternatively, the spent Claus catalyst can be treated thermally and/orchemically to remove, or reduce to an acceptable level, any hydrocarbonsthat may originally have been be present.

DETAILED DESCRIPTION OF THE INVENTION

The methods and compositions of the preferred embodiments of using thespent Claus catalyst are described in the context of the examples whichfollow. These examples are directed to the utilization of spent Clauscatalyst as a raw material in the manufacture of Types I, II and Vcement.

In preparing the representative samples for this embodiment of theprocess and product of the invention, spent Claus catalyst having a highalumina content was blended with other conventional ingredients tomanufacture a Portland cement of the type used in the construction ofinfrastructure and other building projects. The cured concrete productwas acceptable in terms of its physical performance characteristics.

In order to determine the composition of spent Claus catalyst particles,four spent Claus catalyst samples from different petroleum processingplants and processes were analyzed utilizing X-ray fluorescencespectrometry. The catalysts were presumed to be from different batchesand may have been from different commercial producers. Each of thesamples was ground in an agate pulverizer to a fineness of about 100mesh and mixed thoroughly before being exposed to the X-ray beam. Thesesamples were composed mainly of aluminum, carbon, sulfur, hydrocarbonand traces of other metals. Sample A contained higher aluminum oxidecontent and less carbon and hydrocarbon components when compared toother spent catalyst samples. The alumina content of the samples rangedfrom about 74% to 84% by weight.

The composition in weight percent of four spent Claus catalysts asreceived are reported in Table 1.

TABLE 1 Sample 1 Sample 2 Sample 3 Sample 4 Compound Wt % Wt % Wt % Wt %SiO₂ <.01 <.01 <.01 0.01 Al₂O₃ 83.74 74.84 75.31 74.35 Fe₂O₃ <.01 <.01<.01 <.01 CaO 0.09 0.08 0.07 0.08 MgO 0.23 0.20 0.20 0.20 SO₃ 0.09 0.270.29 0.20 Na₂O 0.28 0.25 0.26 0.25 K₂O <.01 <.01 <.01 <.01 TiO₂ <.01<.01 <.01 <.01 P₂O₅ <.01 <.01 <.01 <.01 Mn₂O₃ 0.01 0.01 0.01 0.01 SrO0.02 0.02 0.02 0.02 Cr₂O₃ <.01 <.01 <.01 <.01 ZnO 0.01 0.01 0.01 0.01L.O.I. (950° C.) 15.54 23.99 23.61 24.44 Total 100.01 99.66 99.77 99.56The Loss on Ignition (L.O.I.) reported above was conducted at 950° C.

Four different cement formulations were prepared using the fourdifferent spent Claus catalysts Samples 1-4 that are composed mainly ofalumina, and were mixed with limestone, sand, clay and iron ore. A fifth(control) mix was prepared from conventional raw materials to producefive typical U.S. type V cements. The tests were conducted at anindependent laboratory and are reported in Table 2. The quantities ofeach ingredient are in grams.

TABLE 2 Control Mix 1 Mix 2 Mix 3 Mix 4 Limestone 1287 1362 1365 13651365 Clay 232 0 0 0 0 Iron Ore 26 35 35 35 35 Sand 0 113 113 113 113Spent Claus Catalyst 0 30 30 30 30 Total 1545 1540 1543 1543 1544The projected mineralogical composition of clinkers, as a percentage(%), is shown in Table 3.

TABLE 3 Typical Range Control Mix 1 Mix 2 Mix 3 Mix 4 C₃S tricalcium 43to 70 60.0 60.0 61.9 60.8 60.0 silicate C₂S dicalcium 11 to 31 16.6 16.316.0 16.1 17.0 silicate C₃A tricalcium 0 to 5 3.6 4.0 4.3 4.3 4.3aluminate C₄AF 10 to 19 10.9 10.9 12.1 12.2 12.2 tetracalciumaluminoferrite

The materials utilized in the formulations of Table 2 were crushed,blended and ground in a porcelain jar mill to the fineness of 85%passing a 76 μm sieve. Briquettes of about 100 grams each were preparedin a Carver hydraulic press. The specimens were pre-heated at 900° C.and fired at 1450° C. in a Blue M high-temperature furnace.

After firing, the clinker briquettes having the composition of Table 3were crushed and ground to a Blaine specific surface of 340 m²/Kg withan addition of 5% Terra Alba gypsum. The resulting cements were analyzedby XRF. The results of this analysis of the cement chemical composition,as wt %, is reported in Table 4.

TABLE 4 Control Mix 1 Mix 2 Mix 3 Mix 4 SiO₂ 20.44 20.85 20.41 21.1121.54 Al₂O₃ 3.47 4.22 4.07 4.18 4.20 Fe₂O₃ 3.61 4.00 3.98 4.07 4.10 CaO64.32 63.76 64.86 63.98 63.69 MgO 2.34 1.90 1.87 1.94 1.98 SO₃ 2.56 2.492.56 2.60 2.59 Na₂O 0.20 0.09 0.09 0.09 0.10 K₂O 0.31 0.26 0.25 0.260.25 TiO₂ 0.21 0.13 0.13 0.14 0.14 P₂O₅ 0.03 0.02 0.02 0.02 0.02 Mn₂O₃0.04 0.04 0.04 0.04 0.04 SrO 0.04 0.04 0.04 0.04 0.04 Cr₂O₃ <.01 <.01<.01 <.01 <.01 ZnO <.01 <.01 <.01 <.01 <.01

The resulting cements were tested for compressive strength in mortarcubes according to ASTM C 109, the results of which are reported inTable 5. The mortar cube strength is in psi.

TABLE 5 Control Mix 1 Mix 2 Mix 3 Mix 4 3 days 2440 2280 2260 2380 24507 days 3620 3080 3140 3010 3300 28 days  4620 4670 4630 5020 5210

The data in Table 5 shows some variations in the strength of cementspecimens, but these variations are not significant and the specimensare considered to be of substantially the same quality. It is evidentthat replacement of clay with the Claus catalyst sand mix did notnegatively affect the cement's performance.

Another analysis was carried out to evaluate burnability of the fourmixing formulations. Burnability is the term used to indicate thereactivity of the kiln feed with respect to forming clinker mineralsduring the burning process, and is usually measured by the free limecontent of the clinker. The lower the temperature at which the targetedfree lime can be obtained, the better is the burnability of the kilnfeed. One procedure for characterizing the burnability of a kiln feed isto perform laboratory burns under standardized conditions and to thenanalyze for the resulting free lime content

Results from such tests can then be compared, and the raw materials andmix compositions giving the best burnability values can be selected bycomparison. Burnability can also be predicted by the chemical andmineralogical parameters of the raw mix.

The burnability of the five mixes described above was evaluatedaccording to the equations developed by F. L. Smidth as follows:FL₁₄₀₀=0.31(LSF−I00)+2.18(Ms−I.8)+0.73Q ₄₅+0.33C ₁₂₅+0.34A ₄₅  (1)FL₁₅₀₀=0.2I(LSF−I00)+I.59(Ms−I.8)+0.40Q ₄₅+0.22C ₁₂₅+0.08A ₄₅  (2)Where:

-   -   FL₁₄₀₀=“Virtual burnability index”, or free lime content        anticipated in a commercial clinker fired at 1400° C.;    -   FL₁₅₀₀=same, at 1500° C.;    -   LSF=lime saturation factor;    -   Ms=silica ratio;    -   Q₄₅=% of quartz>45 μm;    -   C₁₂₅=% of calcite>125 p.m; and    -   A₄₅=% of insoluble particles>45 μm.

The importance of this determination is its use in evaluating the effectof possible changes in (1) chemical composition, or (2) mineralogy andfineness, or (3) both.

Both analytical and direct empirical approaches were used. Fordetermination of the parameters included in the equations (1) and (2),the chemical parameters of the lime saturation factor and silica ratiowere taken from the chemical analyses. For measurement of the particlesizes, the material was screened through Nos. 120 and 325 mesh sieves,being 125 and 45 μm, respectively. The +45 μm residue was treated withacetic acid to dissolve the carbonate particles. The residues wereexamined microscopically by a point-count technique and the particlesizes in raw mixes are reported in Table 6.

TABLE 6 Control Mix I Mix 2 Mix 3 Mix 4 Residue >125 μm 1.4 5.8 6.3 6.06.2 Calcite in residue 76.3 50.3 54.3 55.3 56.3 Calcite >125 μm in total1.1 2.9 3.4 3.3 3.5 sample >45 μm residue (acid wash) 5.2 9.7 9.4 10.210.1 Quartz in residue 26.6 36 42.3 38.6 29 Acid-insoluble particles73.4 64 57.7 61.4 71 >45 μm in residue Quartz >45 μm in total 1.4 3.5 43.9 2.9 sample Other acid-insoluble 3.8 6.2 5.4 6.3 7.2 particles >45 μmin total sampleThe results of calculations are shown in Table 7 as the virtualburnability index of the mixes

TABLE 7 FL Control Mix 1 Mix 2 Mix 3 Mix 4 1400 2.87 5.81 6.07 6.27 5.911500 1.32 2.75 3.00 3.01 2.72

Direct free lime determination was conducted using the followingprocedure. Raw meal pellets of about 13 mm in size were prepared anddried, and pre-calcined at 900° C. The pellets were further fired at1350° C., 1400° C. and 1450° C. for 20 minutes in an electric furnace.Free CaO, or free lime content was analyzed as the principal criterionof the lime digestion which is reported in Table 8. The fired sampleswere also subjected to microscopic examination as will be describedbelow.

TABLE 8 ° C. Control Mix 1 Mix 2 Mix 3 Mix 4 1350 0.76 1.48 2.26 1.541.5 1400 0.42 0.72 0.69 0.58 0.74 1450 0.35 0.50 0.51 0.43 0.60

When analyzing the data from Tables 7 and 8, it is to be noted that, dueto the vastly different firing conditions in a commercial kiln and alaboratory furnace, the “virtual burnability” values in Table 7 are notidentical to the actual free lime in Table 8. However, the valuesclearly demonstrate the trends in the burnability of the mixes. In theexperimental burns, all mixes produced equally acceptable results.However, the data indicates that the control mix possessed betterburnability characteristics due to the finer sizes of quartz andsilicate particles. Generally, poor quartz grindability can lead to thenecessity of finer grinding raw materials containing sand and similaringredients to avoid problems in burning.

Microscopic examination was also undertaken to detect any irregularitiesin the clinker formation. The purpose of this microscopic examinationwas to assist in the selection of the proportions of ingredients in thefinal cement formulations. For the purpose of this examination, thesamples were identified as set forth in Table 9.

TABLE 9 Sample ID Mix Temperature, ° C. C-135 Control 1350 C-140 Control1400 C-145 Control 1450 1-135 1 1350 1-140 1 1400 1-145 1 1450 2-135 21350 2-140 2 1400 2-145 2 1450 3-135 3 1350 3-140 3 1400 3-145 3 14504-135 4 1350 4-140 4 1400 4-145 4 1450

The results of the microscopic examination indicated that spent Clauscatalysts samples using clay did not lead to any abnormalities in theclinker microstructure. Certain characteristics such as non-uniformdistribution and formation of belite nests can be attributed to therelatively coarse sizes of the quartz grains. Under actual productionconditions, the meal fineness can be adjusted to accommodate thecompositional changes.

As will be understood from the above description and data, spent Clauscatalyst can be successfully used to produce a high quality Portlandcement for use in the construction of facilities of various types. Nospecial processing is required prior to addition of the spend Clauscatalyst to the Kiln and the processing and handling of the clinkers cancontinue as with the prior art formulations. The invention thus meetsthe objectives of disposing of significant quantities of a material thathas been considered a waste by-product of the petroleum refiningindustry in an economical and environmental acceptable manner.

A further aspect of the invention is directed to the use of spent Clauscatalyst particles as an additive to modify the curing characteristicsof an oilwell cement slurry for shallow casing cementing.

It has been found that when spent Claus catalyst is added to shallow iscasing cement slurries, there is an increase in the thickening time ofthe shallow casing cement slurry, as measured by API10 procedures. Theobserved increase in thickening time occurred at additive levels of 0.1%and 2.0% of the spent catalyst.

In the practice of this preferred embodiment of the invention, the spentcatalyst was ground or pulverized to particles in the size range of from6.8-10.4 microns (μm) before addition to the slurry.

Table 10 reports the data from the evaluation of oilwell slurry cementsamples with and without the additive.

TABLE 10 Properties Sample A Sample B Sample C Sample D Blank CI-G SACK1.00 1.00 1.00 1.00 1.00 TWTR % VOL 100 100 100 100 100 SCC Additive0.100 1.00 2.00 5.00 0.00 % BWOC Thickening Increase Decrease IncreaseDecrease 105 Time - minutes −119

Blending spent catalyst into the cement slurry of shallow casing cementjobs gives an increase in the thickening time to 119 minutes compared to105 minutes for unmodified class G cement formulations.

In order to adapt this spent catalyst for use as an additive in oilwellcement, the combined mixture of oilwell cement and spent catalyst mustbe easily pumpable for a sufficient time to allow proper placement ofthe slurry in the well. The desired consistency for the pumpable cementcan be achieved by pulverizing the spent catalyst, which is in sphericalform, to fine particles in the range of about 6.8-10.4 μm.

Although the above examples and description is comprehensive, it isintended to be illustrative and various modifications to the methods andcompositions described will be apparent to those of ordinary skill inthe art. The full scope of the invention is therefore to be determinedwith reference to the claims that follow.

1. A method of varying the thickening time of a class G cement used incompleting a subterranean wellbore, the method comprising: preparing aslurry of the class G cement; adding ground alumina-containing spentClaus catalyst to the slurry and mixing it to form a uniformcomposition; and disposing the composition containing the spent Clauscatalyst into the wellbore.
 2. The method of claim 1 in which the spentClaus catalyst is added to a class G cement that is in the form of apumpable slurry.
 3. The method of claim 1 in which the addition of theground spent Claus catalyst increases the thickening time of the cement.4. The method of claim 1 in which the spent Claus catalyst is in theform of ground particles in the size range of from 6.8 to 10.4 microns.5. The method of claim 4 in which the spent Claus catalyst has beentreated to reduce any residual hydrocarbons remaining in the catalystadditive.
 6. The method of claim 5 in which the spent Claus catalyst hasbeen subjected to a treatment selected from the group consisting of achemical process, a thermal process, and a combination of chemical andthermal processes.